Remotion Arbitrary File Write Vulnerability in Video Library

Remotion v4.0.409 contains a critical arbitrary file write vulnerability (CVE-2026-30121, CVSS 9.1) that allows attackers to write files to arbitrary locations on affected systems. This vulnerability impacts developers and organizations using Remotion, a popular open-source library for creating videos programmatically. The arbitrary file write capability is particularly dangerous because it can lead to remote code execution, privilege escalation, or deployment of malware—attackers could overwrite critical system files, inject malicious code into application directories, or plant backdoors for persistent access. Any system running the vulnerable version of Remotion with untrusted input or network exposure faces immediate risk.

While this CVE doesn't map to established MITRE ATT&CK techniques in the current framework, Casky's Claude-powered analysis would identify attack patterns consistent with Defense Evasion (T1036 - Masquerading), Persistence (T1547 - Boot or Logon Autostart Execution), and Execution (T1059 - Command and Scripting Interpreter) once the arbitrary file write is weaponized. Security practitioners using Casky would detect suspicious file creation events in unexpected directories, particularly writes to system paths, configuration directories, or application startup folders. The platform's extended reasoning would correlate input validation failures with file system modifications, helping teams distinguish legitimate Remotion operations from exploitation attempts and prioritize remediation of this critical vulnerability across their infrastructure.